Method for the production of aryl alkenes

ABSTRACT

The present invention relates to a novel oxidative coupling arenes with olefins to yield aryl alkenes, which uses ruthenium (Ru) or Osmium (Os) compounds as catalysts.

FIELD OF THE INVENTION

The present invention relates to a novel oxidative coupling of areneswith olefins to yield aryl alkenes, which uses ruthenium (Ru) or osmium(Os) compounds as catalysts.

BACKGROUND OF THE INVENTION

Catalytic carbon-carbon bond formation by C—H activation is a topic ofmuch current interest. Significant progress has been made in recentyears in the development of synthetically useful catalytic addition ofarenes to alkenes to give the saturated alkyl arenes (Murai et al, 1993;Kakiuchi et al, 1996; Jia et al, 2000a, 2000b; Matsumoto et al, 2000a).

Catalytic oxidative coupling of arenes with alkenes to give arylalkenes, in which the double bond is preserved, is a highly desirablegoal. Such a reaction, which does not require the utilization of areactive substituent, and does not produce waste, may have an advantageover other methods for the preparation of aromatic alkenes, such as thewell-known Heck reaction for the vinylation of aryl halides.Stoichiometric coupling of olefins with arenes promoted by Pd(II) iswell known (Moritani et al, 1967; U.S. Pat. No. 3,674,884, 1972).

Tsuji et al (1984) and lately Fujiwara et al (1996) and Mikami et al(1999) have demonstrated catalysis by utilizing peroxides as oxidants intheir systems. While good catalytic activity was achieved with somealkenes, acrylates resulted in low activity (˜10 turnovers). The use ofperoxide oxidants and acetic acid solvent in these systems isproblematic from the industrial point of view. Attempts to use O₂ or airresulted in low activity in intramolecular (Miura et al, 1997, 1998) andintermolecular (Fujiwara et al, 1969, 1976; Asano et al, 1970; Shue,1972; U.S. Pat. No. 3,855,329) coupling and alkene oxidation took placein the intermolecular reaction.

Another approach utilizing Rh carbonyl clusters under high (20-30 atm)CO pressure (Hong et al, 1984) resulted in modest catalytic activitywith concomitant hydrocarbonylation of the alkene. Low catalyticactivity was reported for the Rh-catalyzed photochemical coupling ofarenes with alkenes, in which concomitant hydrogenation of the alkenetook place and biaryls were formed as by-products (Sasaki et al, 1988;JP 1193241). A very low yield Rh catalyzed oxidative phenylation ofethylene to styrene was reported (Matsumoto et al, 2000b; U.S. Pat. No.6,127,590).

SUMMARY OF THE INVENTION

It has now been found according to the present invention that arylalkenes can be produced by reaction of arenes with olefins in thepresence of ruthenium (Ru) or osmium (Os) compounds as catalysts. Thereaction can be carried out in the presence of molecular oxygen as theoxidant or in the absence of O₂, in which case the alkene itself servesas the oxidant. Reasonable turnover numbers were achieved.

The present invention thus relates to a method for the production of anaryl alkene comprising reacting an arene with an olefin in the presenceof a Ru or Os compound as catalyst. An advantage of the process of thepresent invention using Ru or Os catalysts is the absence of thenecessity of an acid solvent or a peroxide. Furthermore, compared to theprior art process using Rh catalysts and CO, much lower pressure of COmay be used.

In one embodiment, the reaction is carried out in the presence ofmolecular oxygen. The addition of a catalytic amount of hydroquinone orof a quinone such as, but not being limited to, benzoquinone, improvesthe yield of the reaction. The reaction may be carried out in an inertatmosphere but it is preferably carried out in an atmosphere containingCO. CO pressures are between 0 to about 100 atm, preferably between 1 to10 and most preferably between 6 to 8 atm.

While it is expected that any ruthenium or osmium compound could be usedin accordance with the present invention, preferred examples ofruthenium compounds that may be used include, but are not limited to,RuCl₃.3H₂O, [Ru(CO)₃Cl₂]₂, [(η⁶-C₆ H₆)RuCl₂]₂,[(η⁶-C₆H₆—Ru(H₂O)₃](F₃CSO₃)₂, Ru(NO)Cl₃.5H₂O, Ru(F₃CCOCHCOCF₃)₃ andRu₃(CO)₁₂. In one preferred embodiment, the ruthenium compound isRuCl₃.3H₂O.

Preferred examples of osmium compounds that may be used according to theinvention include, but are not limited to, OsCl₃.3H₂O, OsO₄,[Os(CO)₃Cl₂]₂, [(η⁶-C₆H₆)OsCl₂]_(b 2), Os(NO)Cl₃.5H₂O ,Os(F₃CCOCHCOCF₃)₃ and Os₃(CO)₁₂.

Most of the Ru and Os compounds present a higher catalytic activity in aCO atmosphere but the compounds Ru(F₃CCOCHCOCF₃)₃, Ru₃(CO)₁₂ andOs₃(CO)₁₂ exhibit catalytic activity in the absence of a CO atmosphere.

In one embodiment, the method of the invention is used for theproduction of an aryl alkene of the formula:Ar—CR₁═CR₂—R₃wherein Ar is an aryl radical and R₁, R₂, R₃ independently of each otherrepresent H, alkyl, aryl, alkoxycarbonyl or aryloxycarbonyl.

As used herein, the term “aryl” includes carboaryl radicals such as, butnot being limited to, phenyl and naphthyl, and heteroaryl radicals suchas, but not being limited to, furyl, thienyl, the aryl radical beingoptionally substituted by one or more halogen atoms, alkyl optionallysubstituted by one or more halogen atoms or alkoxy, and the term “arene”relates to the aromatic compound from which the aryl radical is derived,e.g., benzene, naphthalene furan, thiophene, that may be substituted asindicated for the aryl radical.

As used herein, the term “alkyl” for an alkyl radical itself or part ofan alkoxy radical includes straight and branched radicals having up to25 carbon atoms, preferably up to 20, more preferably up to 10, and mostpreferably up to 6 carbon atoms such as methyl, ethyl, propyl, butyl,pentyl and hexyl, wherein said alkyl may be optionally substituted byhalogen such as fluoro, chloro and bromo, or by alkoxy.

In one embodiment, the aromatic compound may be substituted by one ormore alkyl or fluoroalkyl, preferably methyl or CF₃, radicals, and maybe, for example, toluene or xylene. In another embodiment, the aromaticcompound may be substituted by an alkoxy, preferably methoxy, radical,and may be, for example, anisole or 2-methoxynaphthalene. In a furtherembodiment, the aromatic compound may be substituted by a halogen suchas fluoro, chloro and bromo, and may be, for example, chlorobenzene.

When R₁, R₂, R₃ are hydrogen the reaction is carried out with ethylene.Thus when the arene is benzene the end product is styrene and when thearene is naphthalene the end product is vinylnaphthalene. When R₁, R₂,R₃ are alkyls, the end product will be an alkenyl arene. R₁, R₂, R₃ mayalso be alkyl substituted by one or more halogen atoms such as chloro,bromo, and preferably fluor. In one example as shown herein benzene isreacted with 3,3,4,4,5,5,6,6-nonafluorohex-1-ene thus producing(3,3,4,4,5,5,6,6-nonafluorohex-1-enyl)benzene.

In one preferred embodiment of the invention R₁is an alkoxycarbonylradical such as ethoxycarbonyl and, more preferably, methoxycarbonyl andR₂, R₃ are hydrogen. Thus for the preparation of an alkyl cinnamate,benzene is reacted with an alkyl acrylate such as methyl or ethylacrylate. When a substituted benzene or naphthalene compound is reactedwith an alkyl acrylate, the corresponding alkyl 2-propanoate derivativesare obtained such as methyl 3-(chlorophenyl)-2propanoate, methyl3-methoxyphenyl-2-propanoate, methyl 3tolyl-2-propanoate, methyl3-(2,5-dimethylphenyl)-2-propanoate, methyl 3-(2-naphthyl)-2-propanoateand methyl 3-(2- or 6- or 7-methoxy-2-naphthyl)-2-propanoate, that areproduced by reacting an arene selected from chlorobenzene, anisole,toluene, pxylene, naphthalene and 2-methoxynaphthalene, respectively,with methyl acrylate.

In another preferred embodiment of the invention R₁ is an alkoxycarbonylradical, preferably, methoxycarbonyl, R₂ is hydrogen and R₃ is acarboaryl, preferably, phenyl. Thus for the preparation of an alkyl3,3-diaryl propanoate, an arene is reacted with an alkyl cinnamate suchas methyl or ethyl cinnamate. In one example as shown herein benzene isreacted with methyl cinnamate, thus producing methyl 3,3-diphenylpropanoate.

Oxygen is preferably added to the reaction at 0-10 atmospheres, morepreferably 1-2 atmospheres, and the temperature of the reaction ispreferably 50-250° C., and more preferably 150-180° C. At temperaturesabove 250° C., the reaction will still take place, but some amount ofdecomposition will result. At lower than 50° C., the reaction will stilltake place, but the turnover will become unproductively small.Similarly, at an O₂ pressure above 10 atm, the reaction will still beexpected to take place, but the process would not be industriallypractical.

The aryl alkenes produced by the process of the invention are usefulintermediates particularly for the pharmaceutical industry.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a novel oxidative coupling of arenes witholefins, which may optionally use molecular oxygen as the oxidant. Goodcatalytic activity is exhibited by the Ru compounds RuCl₃.3H₂O,[Ru(CO)₃Cl₂]₂, [(η⁶-C₆H₆)RuCl₂]₂, Ru(NO)Cl₃.5H₂O and Ru(F₃CCOCHCOCF₃)₃under a pressure of 2 atm of O₂ and 6.1 atm of CO at 180° C. In theabsence of O₂, the alkene itself serves as the oxidant and the couplingis accompanied by a parallel alkene hydrogenation. The reaction isaccelerated by electron donating substituents on the arene.

Notably, the dehydrogenative coupling proceeds either under O₂(Equation 1) or in an inert atmosphere (Equation 2). In absence of O₂the olefin itself serves as an oxidant and, for example, when benzene(Ar=phenyl) is reacted with methyl acrylate (R₁ is —COOCH₃, R₂, R₃ ═H) a1:1 ratio of cinnamate: propanoate is obtained. In comparison, under 2atm of O₂ the cinnamate yield is doubled and a ratio of about 3:1 ofcinnamate: 2-propanoate is obtained (see Table 1). Essentially noorganic carbonylation products are observed. The product turnover numberincreases with CO pressure up to 6.1 atm, beyond which further pressureincrease has no beneficial effect. Various arenes and alkenes arereactive (see Table 3). Alky acrylates are by far the most active of theolefins tested.

The invention will now be illustrated by the following non-limitingExamples.

EXAMPLE 1 Oxidative Coupling of Benzene with Acrylate Esters

1A. With Ru Complexes as Catalysts

A solution containing 8 ml of benzene, 0.02 mmol of RuCl₃.3H₂O (1) and 5mmol of methyl or ethyl acrylate in a Fischer-Porter glass reactor waspressurized with 6.1 atm CO and 2 atm O₂ and heated to 180° C. withstirring for 48 hours, thus producing methyl or ethyl cinnamate. Theresults are shown in Table 1.

Addition of a catalytic amount of hydroquinone (HQ) (Entries 6 and 7) orquinone improved the yield, the turnover number and the mass balance ofthe reaction. Ten or 20 eq of HQ (relative to Ru) had a similar effect.Addition of a radical trap (galvinoxyl) does not retard the reaction andit proceeds as well in the dark (Entry 3 in Table 1).

TABLE 1 Oxidative Coupling of Benzene with Acrylate Esters Yield YieldResidual Pro Cinna- Mass Acrylate panoate mate % Balance EntryConditions^(a) % % [TON] % 1 MA*, 2 atm O₂ 22 10 35 67 [88]  2 MA*, noO₂ 41 20 20 81 [50]  3 MA*, no O₂, no light, 38 23 23 84 0.2 mmolgalvinoxyl [57]  4 MA*, 2 atm O₂ 23 3 35 63 5 eq CuO [88]  5 EA**, 2 atmO₂ 26 10 30 66 [75]  6 EA**, 2 atmo O₂, 21 19 40 80 10 eq HQ [100] 7EA**, 2 atm O₂, 17 21 42 80 20 eq HQ [105] ^(a)Reaction conditions: asolution containing 8 mL of benzene, 0.02 mmol of 1 and 5 mmol ofacrylate ester in a Fischer-Porter glass reactor is pressurized with 6.1atm CO and 2 atm O₂ and heated to 180° C. with stirring for 48 hours.*MA = methyl acrylate. **EA = ethyl acrylate. TON = turnover number.Yields are based on acrylate ester.1B. With [η⁶-C₆H₆—Ru(H₂O)₃](F₃CSO₃)₂ as Catalyst with 1 atm of CO

A solution containing 8 ml of benzene, 0.02 mmol of[η⁶-C₆H₆—Ru(H₂O)₃](F₃CSO₃)₂ and 5 mmol of ethyl acrylate in aFisher-Porter glass reactor was pressurized with 1 atm CO and 7.1 atm ofinert gas (e.g., Argon or N₂) and heated to 180° C. with stirring for 48hours. GC analysis revealed formation of 1.1 mmol (E)-ethyl cinnamate(22% yield, 55 TON) and 1.3 mmol ethyl propanoate (26% yield, 65 TON).

1C. With Ru(CF₃COCHCOCF₃)₃ or OS₃(CO)₁₂ or Ru₃(CO)₁₂ as Catalystswithout CO Pressure

A solution containing 8 ml of benzene, 0.02 mmol of catalyst (per metalcenter) and 5 mmol of ethyl acrylate in a Fischer-Porter glass reactorwas pressurized with 2 atm of O₂ and 6.1 atm of inert gas (e.g., Argonor N₂) and heated to 180° C. with stirring for 48 hours. The results areshown in Table 2.

TABLE 2 Oxidative Coupling of Benzene with Acrylate Esters without COPressure^(a,b) Yield Yield Residual Pro- Cinna- Mass Acrylate panoatemate % Balance Entry Catalyst % % [TON] % 8 Ru(CF₃COCHCOCF₃)₃ 61 4 3 68[6] 9 Os₃(CO)₁₂ 55 6 3 64 [6] 10 Ru₃(CO)₁₂ 49 3 2 54 [4] ^(a)Reactionconditions: a solution containing 8 mL of benzene, 0.02 mmol of catalyst(per metal center) and 5 mmol of ethyl acrylate in a Fischer-Porterglass reactor is pressurized with 6.1 atm Ar and 2 atm O₂ and heated to180° C. with stirring for 48 hours. Yields are based on ethyl acrylate.^(b)Other catalysts mentioned above gave under this conditions about 1TON.1D. With Os Complexes as Catalysts

A solution containing 8 ml of benzene, 0.02 mmol of OsCl₃.xH₂O(2) orOsO₄ (3) and 5 mmol of ethyl acrylate in a Fischer-Porter glass reactorwas pressurized under 2 atm of O₂ and 6.1 atm of argon and heated to180° C. with stirring for 48 hours, thus producing ethyl cinnamate. Theresults are shown in Table 3.

TABLE 3 Oxidative Coupling of Benzene with Ethyl Acrylate Utilizing OsCompounds Yield Yield Residual Pro- Cinna- Mass Acrylate panoate mate %Balance Entry Conditions^(a) % % [TON] % 1 2, 2 atm O₂ and 6.1 26 19 1863% atm CO [44] 2 3, 2 atm O₂ and 6.1 73 6.5  6 85.5 atm CO [15]^(a)Reaction conditions: a solution containing 8 mL of benzene, 0.02mmol of 2 or 3 and 5 mmol of ethyl acrylate in a Fischer-Porter glassreactor is pressurized with CO and O₂ and heated to 180° C. withstirring for 48 hours. Yields are based on acrylate ester.

EXAMPLE 2 Oxidative Coupling of Various Arenes with Olefins Under O₂

In a typical reaction protocol, an 80 mL glass pressure tube is chargedwith 90 mmol of arene, 0.02 mmol of RuCl₃.3H₂O, 0.2 mmol HQ and 5 mmolof acrylate. The reactor is then evacuated and then pressurized with 6.1atm CO and 2 atm O₂ and heated to 180° C. with stirring for 48 hours.The liquid phase is sampled and analyzed by gas chromatography, massspectroscopy and HNMR spectroscopy at the end of the reaction. Theproducts are characterized by comparison with authentic samples. In thisway, methyl acrylate was reacted with benzene, chlorobenzene, toluene,anisole, p-xylene, naphthalene and 2-methoxynaphthalene, and ethylene,methyl cinnamate and H₂C═CH(CF₂)₃CF₃ were reacted with benzene. Theresults are shown in Table 4.

TABLE 4 Oxidative Coupling of Various Arenes with Olefins under O₂ ^(a)Yield Product % Entry Arene Olefin p:m:o ratio [TON] 1 chlorobenzene MA(E)-Methyl 3-(chlorophenyl)propanoate 34  1:2:0 [86] 2 benzene MA(E)-Methyl cinnamate 41  (105] 3 toluene MA (E)-Methyl3-(tolyl)propanoate 44  1:1.6:0 [110] 4 anisole MA (E)-Methyl 3- 47 (methoxyphenyl)propanoate [118] 1: 1. 3 :1. 05 5 benzene EthyleneStyrene 3.0 [7.5] 6 benzene H₂C = CH(CF₂)₃CF₃(3,3,4,4,5,5,6,6,6-Nonafluoro-hex-1- 4.1 enyl) benzene (5.4] 7 p-xyleneMA (E)-Methyl 3-(2,5-dimethylphenyl) 2.3 propanoate [5.7] 8 p-dichloro-MA No coupling product   0 benzene 9 naphthalene MA (E)-Methyl3-(2-naphthyl)propanoate  28 [70] ^(a)The reaction was carried out asdescribed above in Example 2. Entry 5 was carried out under 3.4 atm ofCO and 3.4 atm of ethylene. In Entry 6, 2.63 mmol of H₂C = CH(CF₂)₃CF₃were used. (E) is defined according to Stretweiser et al (1972).

The reaction is accelerated by electron donating substituents on thearene.

In summary, a novel Ru- and Os-catalyzed oxidative coupling of areneswith olefins to produce aryl alkenes, which can either directly utilizedioxygen or can utilize the alkene as oxidant and results in reasonableturnover numbers, has been disclosed.

REFERENCES

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1. A method for the production of an aryl alkene, comprising reacting anarene with an olefin in the presence of a Ru or Os compound as catalyst,such that an aryl alkene is produced.
 2. A method according to claim 1,wherein the reaction is carried out in the presence of molecular oxygen.3. A method according to claim 2, wherein the reaction is carried out inthe presence of a hydroquinone or a quinone.
 4. A method according toclaim 1, wherein the reaction is carried out in an atmosphere containingCO.
 5. A method according to claim 4, wherein the CO atmosphere has a COpressure of up to about 100 atm.
 6. A method according to claim 5,wherein said CO pressure is 6-8 atm.
 7. A method according to claim 1,wherein the ruthenium compound is selected from the group consisting ofRuCl₃.3H₂O, [Ru(CO)₃Cl₂]₂, [(η⁶-C₆H₆)RuCl₂]₂,[(η⁶-C₆H₆—Ru(H₂O)₃](F₃CSO₃)₂, Ru(NO)Cl₃.5H₂O, Ru(F₃CCOCHCOCF₃)₃ andRu₃(CO)₁₂.
 8. The method according to claim 7, wherein the rutheniumcompound is RuCl₃.3H₂O.
 9. A method according claim 1, wherein theosmium compound is selected from the group consisting of OsCl₃.xH₂O,[Os(CO)₃Cl₂]₂, [(η⁶-C₆H₆)OsCl₂]₂, Os(NO)Cl₃.5H₂O, Os(F₃CCOCHCOCF₃)₃ andOSO₄.
 10. The method according to claim 9, wherein the osmium compoundis OsCl₃.xH₂O.
 11. A method according to any one of claim 1, for theproduction of an aryl alkene of the formula:Ar—CR₁═CR₂—R₃ wherein Ar is an aryl radical and R₁, R₂, R₃ independentlyof each other represent H, alkyl, aryl, alkoxycarbonyl oraryloxycarbonyl.
 12. A method according to claim 11, wherein Ar is acarboaryl, or a heteroaryl radical, the aryl radical being optionallysubstituted by one or more halogen atoms, alkyl optionally substitutedby one or more halogen atoms, or alkoxy.
 13. A method according to claim12, wherein said alkyl or alkoxy radical has up to 25 carbon atoms. 14.A method according to any one of claim 1 for the preparation of an alkylcinnamate which comprises reacting benzene with an alkyl acrylate.
 15. Amethod according to claim 14 for the preparation of methyl cinnamatewhich comprises reacting benzene with methyl acrylate.
 16. A methodaccording to claim 14 for the preparation of ethyl cinnamate whichcomprises reacting benzene with ethyl acrylate.
 17. A method accordingto any one of claim 1 for the preparation of an alkyl aryl-2-propanoatewhich comprises reacting an arene with an alkyl acrylate.
 18. A methodaccording to claim 17 for the preparation of an alkyl aryl-2-propanoateselected from the group consisting of methyl3-(chlorophenyl)-2-propanoate, methyl 3-(methoxyphenyl)-2propanoate,methyl 3-(tolyl)-2-propanoate, methyl3-(2,5-dimethylphenyl)-2-propanoate, methyl 3-(2-naphthyl)-2propanoateand methyl 3-(2- or 6- or 7-methoxy-2-naphthyl)-2propanoate, whichcomprises reacting an arene selected from the group consisting ofchlorobenzene, anisole, toluene, p-xylene, naphthalene and2-methoxynaphthalene, respectively, with methyl acrylate.
 19. A methodaccording to any one of claim 1 for the preparation of styrene whichcomprises reacting benzene with ethylene.
 20. A method according to anyone of claim 1 for the preparation of(3,3,4,4,5,5,6,6,6-nonafluoro-hex1-enyl)benzene which comprises reactingbenzene with H₂C═CH(CF₂)₃CF₃.
 21. A method in accordance with claim 12,wherein Ar is phenyl or naphthyl.
 22. A method in accordance with claim12, wherein Ar is furyl or thienyl.
 23. A method in accordance withclaim 13, wherein said alkyl or alkoxy radical has up to 20 carbonatoms.
 24. A method in accordance with claim 13, wherein said alkyl oralkoxy radical has up to 10 carbon atoms.
 25. A method in accordancewith claim 13, wherein said alkyl or alkoxy radical has up to 6 carbonatoms.